Method of grinding pistons



- April 23, 1940- A. L. NELSON I 7 METHOD OF GRINDING PISTONS 2 Sheets-Shet 1 4 Filed llay 28. 1936 INVENTOR April 23, 1940. NELSQN 2,197,940

METHOD OF GRINDING PISTONS Filed may 28. 1936 2 Sheets-Sheet 2 INVENTOR. flDOAP/l A. NELSON.

ATTO

Patented-Apr. 23, 1940 METHOD or GRINDING rrs'rons Adolph L. Nelson, Detroit, Mich., assignor to Bohn Aluminum & Brass Corporation, Detroit, Mich, a corporation of Michigan Application May 28, 1936,Serial No. 82,178

Claims. (Cl. 51-2'78) This invention relates to a method of manufacturing pistons for internal combustion engines, particularly pistons having oval skirts.

' In a known method of making pistons oval by 5 so-called centerless grinding the piston is not held on centers but is merely pushed against the grinding wheel by pressure applied to. the side opposite the grinding wheel. Beforesubjecting a piston to this method of grinding it is customary to first turn down the head of the piston to a diameter smaller than the minor axis of the oval to be later given to the skirt. The result isthat during the oval grinding the head is not touched by the grinding wheel, but the entire pressure l is carried by the skirt both on the grinding side and on the-support side.

This method runs into difficulties when oval grinding is to be applied to' a piston in which the parts of the skirt below the head and adjacent to the pin bosses are relieved or cut away, as for example in U. S. Patent No. 1,401,899 to Fekete. Such a piston does not furnish support at the upper end of the skirt in line with the axis of the pin bosses. By the method of the present invention the head andskirt are simultaneously ground oval, thus using the head for support and permitting accurate grinding of any piston having reliefs. The head maybe ground either smaller than the skirt or of the same size. Other objects and advantages of the invention will become apparent as the description proceeds.

While preferred forms of the invention are disclosed herein for purposes of illustration it should be understood that various changes may be made in the method without departing from the spirit of the invention as herein set forth and claimed.

In the drawings:

Fig. 1 is a diagrammatic view illustratingone manner in which the piston may be ground.

Fig. 2 is a plan view partly broken away illustrating one form-of the improved process.

Fig. 3 is a view similar to Fig. 2 but showing a modification of the process.

Fig. 4 is a view similar to Fig. 2 but showing a further modification.

Fig. 5 is a view similar to Fig. i-but showing a modified means for pressing the piston against the grinding wheel. I

The general arrangement of the parts in one process of "centerless grinding is shown in Fig. 1, Where It is the grinding wheel, H the-piston, 12 the follower wheel, and Ida stationary rest. The rotating parts move in alternate directions,

56 so that if the grinding wheel It moves in a counterclockwise direction, the piston will rotate in a clockwise direction and the follower l2 in a counterclockwise direction, as shown in the drawings. The grinding wheel is cylindrical and the follower wheel is oval with the major axis indi- 5 cated in Fig. l. The piston in its rough cylindrical shape is placed between these wheels on a fixture geared to rotate at the same speed with the follower: wheel, but oppositely thereto. The follower wheel presses the piston against the 10 grinding wheel, with the result'that the piston assumes an oval shape with the major axis of the pistonat right angles to the major axis of the follower wheel. v

In Fig. 2 the process of the present invention 15 is shown being carried out on a piston having a head M, thrust. faces i5 separated from the head by slots' l6, depending piers l1 carrying piston pin bosses l8, a lower annulus l9, and a pair of chordally disposed plates 20. This piston 20 is described in detail in my-copending application Serial No. 78,346. It should be understood that the process can be used on any design of piston, and that it is particularly advantageous on any piston having reliefs around the bosses, 26 such as the piston shown in U. S. Patent No. 1,401,899 to Fekete.

In grinding the piston illustrated in Fig. 2 it is desired to give the exterior of the skirt a slight oval shape at room temperature, with the major axis of the oval disposed at right angles to the axis of the piston pin bosses. This piston is therefore placed on the fixture with the axis of p the pin bosses arranged parallel to the major axis of the oval follower wheel l2, and is pressed 35 against a stop 2| which keeps it in proper axial. position.

Prior to the oval grinding operation the piston hasbeen put through a turning operation in the course of which a plurality of ring grooves 22 are 40 cut in the periphery of the head, leaving lands 23.

In the form of the invention illustrated in Fig. 2 the lands 23 are ground oval simultaneously with the grinding of the skirt, the finished lands having an oval shape corresponding to the oval 45 shape of the skirt, but of a sufiiciently smaller size v to prevent the major axis from expanding into contact with the cylinder wall. To provide for this operation the grinding wheel [0 is formed with a cylindrical part 22 for grinding the skirt, 50 and with a cylindrical part 23 for grinding the. head, part 23 being sufliciently larger than part 22 to insure proper clearance of the major axis of the head in the cylinder of the engine in which it is to operate. The parts are arranged so so that the step 24 between parts 22" and 23 comes opposite the slots IS.

The follower wheel I2 is formed with an oval part 25 engaging the skirt and with a part 26 having a similar but larger oval shape for engaging the head. Step 21 between parts 25 and 26 also is opposite slots It.

This process is of special application where the amount of oval to be given the skirt is relatively small, so that the, amount of oval given the ring lands will not interfere with the proper functioning of the piston rings, andthe lands can therefore be left oval in the completed piston.

In some cases it may not be desired to grind all of the ring lands oval during the oval-grinding of the skirt. The advantage of using the ring -abrupt-steps 24 and 21 on the grinder and follower wheels respectively. The grinding and follower wheels terminate short of the upper land, and this land can therefore be left with a cylindrical shape larger or smaller than the oval ground lands to suit particular requirements. In some cases it may be desired to turn the oval lands to cylindrical shape during a subsequent operation on the piston.

Fig. 4 illustrates a form of the invention in which the grinding wheel and the oval follower wheel l2 are without steps, and in which one or more lands of the piston head are ground to the same size oval as the skirt. These lands may subsequently be turned to final size.

In the forms of the invention thus far described a follower wheel is used to press the piston against the grinding wheel, but any other suitable means may be used. Thus for example, Fig. shows the piston held against the grinding wheel by a rockable cradle 28 mounted on pivot 29 and carrying one or more rollers 30 engaging the piston and a roller 3| engaging cam 32. The latter is properly formed and geared with the piston-turning mechanism to produce the desired oval contour on the piston. The grinding wheel and rollers 30 may have either uniform contours throughout as do the grinding wheel and follower wheel of Fig. 4, or stepped contours as do the grinding wheeband follower wheels of Figs. 2 and 3.

In connection with the following claims the follower wheel I0 may be considered as a roller.

I claim:'

1. A method of grindinga piston having a head, a skirt with thrust faces, a lower annulus, piston pin bosses and depressed areas about the piston pin bosses; which comprises supporting and rotating the piston; engaging the piston on one side with a grinding wheel which is wider than the length of the piston skirt; engaging the head and skirt simultaneously on the other side with a contact member wider than the length of the piston skirt; causing the line of contact.

between the contact member and the piston to reciprocate relative to the grinding wheel and in'a direction at right angles to the axis of the grinding wheel; and rotating the grinding wheel in a direction opposite to the direction of rotation of the piston; the above elements being so disposed that the grinding wheel and the contact member each engage part of the head, the thrust faces, and the lower annulus of the piston,

thereby grinding all of these parts to oval shape head formed with ring lands and a skirt formed with thrust faces, a lower annulus, piston pin bosses, and depressed areas about the piston pin bosses; which comprises supporting and rotating the piston; engaging the piston on one side with.

a grinding wheel which is wider than the length of the piston skirt; engaging the head and skirt simultaneously on the other, side with a contact member wider than the length of the piston skirt; causing theline of contact between the contact member and the piston to reciprocate relative to the grinding wheel and in a direction at right angles to the axis of the grinding wheel; and rotating the grinding wheel in a direction opposite to the direction of rotation of the piston; the above elements being so disposed that the grinding wheel and the contact member each engage the thrust faces, the lower annulus of the piston, and at least one of the ring lands, thereby grinding all of the parts to oval shape by one operation, the supporting contact of the piston head with the grinding wheel and the contact member serving to steady the grinding operation. thus causing a more accurate grind on the skirt.

3. The method recited in claim 2 in which the grinding wheel and the contact member have enlarged parts which engage the ring lands.

4. A method of grinding a piston having a head formed with ring lands and a skirt formed with thrust faces, a lower annulus, piston pin bosses, and depressed areas about the piston pin bosses; which comprises supporting and rotating the piston; engaging the piston on one side with a grinding wheel which is wider than the length of the piston; engaging the head and skirt simultaneously on the other side with at least one roller which is wider than the length of the piston skirt; causing the line of contact between and all of the ring lands, thereby grinding all,

of the parts to oval shape by one operation, the supporting contact of the piston head with the grinding wheel and the roller serving to steady the grinding operation thus causing a more accurate grind on the skirt.

5. The method recited in claim 4 in which the grinding wheel and the roller have'enlarged parts which engage the ring lands.

ADOLPH L. NELSON. 

